SH7720 Datasheet, PDF (160/1524 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer SuperHTM RISC engine Family / SH7700 Series

Section 3 DSP Operating Unit
Notes: 1. If a TRAPA instruction is used as a repeat detection instruction, an instruction
following the repeat detection instruction is regarded as a return address. In this case, a
control cannot be returned to the repeat control correctly. In a TRAPA instruction, an
address of an instruction following the repeat detection address is regarded as return
address. Accordingly, to return to the repeat control correctly, place a return address
prior to the repeat detection instruction.
2. If a SLEEP instruction is placed following a repeat detection instruction, a transition to
the low-power consumption state or an exception acceptance such as interrupts can be
performed correctly. In this case, however, the repeat control cannot be returned
correctly. To return to the repeat control correctly, the SLEEP instruction must be
placed prior to the repeat detection instruction.
(e) Branch from a repeat detection instruction
If a repeat detection instruction is a delayed slot instruction of a delayed branch instruction or a
branch instruction, a repeat loop can be acknowledged when a branch does not occur in a
branch instruction. If a branch occurs in a branch instruction, a repeat control is not performed
and a branch destination instruction is executed.
(f) Program counter during repeat control
If RC[11:0] ≥ 2, the program counter (PC) value is not correct for instructions two instructions
following a repeat detection instruction. In a repeat loop consisting of one to three instructions,
the PC indicates the correct value (instruction address + 4) for an instruction (repeat start
instruction) following a repeat detect ion instruction but the PC continues to indicate the same
address (repeat start instruction address) from the subsequent instruction to a repeat end
instruction. In a repeat loop consisting of four or more instructions, the PC indicates the correct
value (instruction address + 4) for an instruction following a repeat detect ion instruction, but
PC indicates the RS and (RS +2) for instructions two and three instructions following the
repeat detection instruction. Here, RS indicates the value stored in the repeat start register
(RS). The correct operation cannot be guaranteed for the incorrect PC values.
Accordingly, PC relative addressing instructions placed two or more instructions following the
repeat detection instruction cannot be executed correctly and the correct results cannot be
obtained.
Rev. 3.00 Jan. 18, 2008 Page 98 of 1458
REJ09B0033-0300